#include<iostream>
using namespace std;
class A{
	public:
		virtual void f()=0;
		void g(){this->f();		}
		A(){
		}
};
class B:public A{
	public:
		void f(){cout<<"B:f()"<<endl;
		}
};
int main(){
	B b;
	b.g();
	return 0;
}